Ink printer

ABSTRACT

An ink drop printer system in which ink drops of uniform size and free of secondary drops are formed by pulsing an ink nozzle with a d.c. pulse signal having a slow relaxation or decay time. The trailing edge of the d.c. pulse decreases slowly in amplitude, approximately reaching a base line level prior to the occurrence of the next d.c. pulse. Ink drop size is varied by superimposing a low frequency a.c. signal on the d.c. pulse. Ink drop response time is improved by applying a high frequency signal to the nozzle prior to the application of the d.c. pulse. The pulse signal applied to the nozzle may be derived from the scanning of a piece of copy material in accordance with facsimile principles, from the scanning of material in accordance with television principles, or from the output of a computer logic system.

United States Patent Perel et al.

July 1, 1975 154] INK PRINTER [75] Inventors: Julius Perel, Altadena; John F.

Mahoney, South Pasadena, both of Calif.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Sept. 4, 1973 [21] Appl. No.: 393,760

[52] US. Cl 346/140; 346/75 [51] Int. Cl. G01d 15/18 [58] Field of Search 346/140, 75; l0l/DlG. 13, l0l/l [56] References Cited UNITED STATES PATENTS 3,375,528 3/1968 Klavsons et a1 346/140 3,500,436 3/1970 Nordin 346/75 3,512,177 5/1970 Mutschler et a1 346/140 3,588,332 6/1971 Vaccaro 178/66 3,683,212 8/1972 Zolton 346/140 X 3,739,396 6/1973 Harada et a1, 1. 346/140 3,848,258 11/1974 Mahoney et al. 346/140 D.C. SIGNAL SOURCE I T'T u LUJ.

Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm.lames .l. Ralabate; Terry J. Anderson; Leonard Zalman 5 7 ABSTRACT An ink drop printer system in which ink drops of uniform size and free of secondary drops are formed by pulsing an ink nozzle with a d.c. pulse signal having a slow relaxation or decay time. The trailing edge of the d.c. pulse decreases slowly in amplitude, approximately reaching a base line level prior to the occurrence of the next d.c. pulse. lnk drop size is varied by superimposing a low frequency a.c. signal on the d.c. pulse. lnk drop response time is improved by applying a high frequency signal to the nozzle prior to the application of the d.c. pulse. The pulse signal applied to the nozzle may be derived from the scanning of a piece of copy material in accordance with facsimile principles, from the scanning of material in accordance with television principles, or from the output of a computer logic system.

10 Claims, 4 Drawing Figures LOW FREQUENCY A. C. SIGNAL SOURCE PATBHEDJULI I975 SHEET 1 20 a 2/ uc. I LOW SIGNAL I FREQUENCY SOURCE A.c. SIGNAL 0 SOURCE c :I| E? E -m E $20 I 8 630 D. C. HIGH SIGNAL FREQUENCY SOURCE A.C. SIGNAL SOURCE TJMB-ATEHJUL 1 ms SHEET 2 l3 8 93; l 31 x F1630 M FIG-3C N FIG. 3d M INK PRINTER BACKGROUND OF THE INVENTION Prior art devices for recording with liquid ink are generally of three basic types. The first type operates with physical contact between an ink-fed stylus and a recording surface with the stylus being physically removable from the recording surface on receipt of an appropriate signal. Drawbacks of this system include difficulty associated with physical removal of the stylus under varying conditions of operation. At high operating speeds, such as is associated with a fast flow of intel ligence, a highly damped, relatively non-elastic mechanical system is required which becomes impractical or impossible to construct.

A second of the prior existing types of liquid ink recorders is one in which an ink-fed stylus is maintained in constant contact against a recording surface and is moved relative thereto in order to record information. Like the previously mentioned type, this provides a continuous mark on the recording surface at all times when the stylus and recording surfaces are in contact. This type has been largely limited in practical applications to oscillograph use since mechanical complexity has been regarded as too prohibitive to control a continuously marking stylus for the tortuous configurations necessary for modern, sophisticated writing.

The last of the prior existing types of ink recorders is referred to as ink spitters and includes devices in which ink is projected across a gap from a nozzle point or orifice to a recording medium. One type of ink spitter is known as a continuous flow system in which ink drops are formed continuously in response to pressure and vibration. In the region adjacent to the nozzle there is placed a charging tunnel through which the ink drops are projected and which serves the function of applying charge to selected ink drops in accordance with a desired video signal to be produced. Downstream of the tunnel there is provided a set ofdeflecting plates which have a potential applied thereto. The electric field between the plates acts on the charged drops causing them to be deflected in an amount determined by the charge on the drops and the potential difference between the plates. Downstream of the deflection plates a trough is provided for catching and transferring to a waste reservoir any drops which are not deflected. There is provided also a writing medium which receives the deflected ink drops whereby an image representative of the video signals is provided. Such a system is described in US. Pat. No. 3,373,437.

In addition to requiring an ink waste reservoir and possibly pumping means for transferring ink from the reservoir to the nozzle, with the inherent possibilities of ink spillage and failure of mechanical parts with such a system, the continuous flow ink spitters may not provide fidelity with the video signal. Obviously, if the deflection signal is in the process of rising or falling, or is not present at the time the ink drops pass, the deflection of the drops will not be in accordance with the desired video information to be printed. Further, in order to place separate charges on only selected drops, one must know when the drop separation is occurring or the phasing of the drop formation relative to the video signal. In the absence of control of drop separation time. because of unpredictable phase changes in ink drop formation, the uniformity and the fidelity of the printing are effected adversely.

A second type of ink spitter is known as an "ondemand" system in which ink drops are formed selec tively in accordance with the video signal, with all ink drops formed impinging on the recording medium. Such systems are described in US. Pat. Nos. 3,34 l .859 and 2,143,376. In these systems, a conductive bar is placed behind the writing medium and a voltage of one polarity is applied to the bar, the magnitude of the voltage being insufftcient to draw ink from the nozzle. When it is desired to print, square wave or rectangular wave voltage pulses of the other polarity are selectively applied to the nozzle, and the paper is moved. The resulting electrostatic field between the nozzle and the bar will overcome the liquid surface tension and draw ink from the nozzle to the writing medium.

The desirability of an ink system that uses all ink drops formed for printing is apparent, that is, no ink recirculation is required. Also, on demand ink spitters are desirable because they require only a dual electrode system, that is, a nozzle at one potential and a writing medium backing bar at another potential to produce printing, whereas continuous flow ink spitters require much more complicated equipment and electrostatic deflection techniques. However, heretofore such systems have not produced ink drops of uniform size with the result that print line thickness has varied. Also, such systems often produce secondary or satellite ink drops, that is, a small drop or drops trailing the main drop. These secondary drops register at the recording medium and may also result in poor image resolution.

It is therefore an object of the present invention to provide an improved ink printing system.

It is another object of the present invention to provide an improved on-demand" ink printing system that produces images of high resolution.

It is a further object of the present invention to provide an on-demand" ink printing system that does not produce secondary or satellite ink drops.

In accordance with the invention, ink drops of uniform size and free of satellite drops are formed by pulsing the ink nozzle with a dc. waveform having pulses with a controlled pulse relaxation or decay time. That is, by pulsing the nozzle with a waveform having pulses that have a slowly decreasing trailing edge. Ink drop size, and accordingly line thickness, can be varied by superimposing a low frequency a.c. signal on the dc pulses when they are at the peak signal amplitude. Greater uniformity of ink drop size is achieved by applying a high frequency a.c. signal having a low d.c. value to the nozzle prior to the application of the dc pulse waveform. It is believed that the latter a.c. signal conditions the ink at the exit of the nozzle such that more rapid turn-on or response time is achieved.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing of an arrangement of an ink drop printing system in accordance with the present invention.

FIG. 2 is a schematic drawing of another arrangement ofan ink drop printing system in accordance with the present invention.

FIG. 3 illustrates waveforms applied to the nozzles of the arrangements of FIGS. 1 and 2.

FIG. 4 is a schematic diagram of a circuit of producing high voltage pulses at a high frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, the apparatus includes an elongated ink nozzle 10 containing a quantity of liquid recording ink I2 which is electrically conductive and supplied by a reservoir 8. Ink 12 may be pigment-based or dye-based ink having acceptable specified viscosity, conductivity, and surface tension. The nozzel tapers from a large diameter and terminates in a short capillary tip I4. Since only the small hydrostatic pressure due to the ink head is present, the capillary forces at the tip 14 are not overcome and hence ink does not flow from the nozzle. Instead, a convex bulge or miniscus forms on the nozzle tip I4. A flow in the form of ink drops of very small cross section is produced only when the miniscus is subjected to the action of an elec trostatic field of a certain value. The inner diameter of the tip 14 is typically on the order of 0.15mm, and the outer diameter of the tip I4, which controls the size of the miniscus, is preferably on the order of 025mm. Nozzle I is positioned such that the ink drops emanating from the nozzle are directed toward a recording medium 16 which passes over a grounded platen or backing plate 18.

When inking is to be initiated, an electric field is applied to nozzle to pull ink from the nozzle. This field causes free charges in the ink to migrate to the surface of the miniscus. When a threshold field is impressed across the gap between nozzle 10 and platen 18, the force on these charges is sufficient to disrupt the ink surface, causing droplets of ink to be torn from the miniscus and accelerated toward the recording medium The electrical signal supplied to nozzle 10 by signal source 20 to create the electrostatic field has a controlled time-amplitude relationship or characteristic which produces ink drops of uniform size and ink drops free of secondary drops. Specifically. the signal supplied by source 20 has a slow relaxation or decay time, that is, a trailing edge that decreases in amplitude slowly from a steady, intermediate level. Particularly, the amplitude of the trailing edge of each pulse supplied by source 20 decreases at a rate slower than the rise time of the leading edge of the pulse.

FIG. 3a depicts the pulses of a waveform 22 illustrative of the signal supplied by source 20 in accordance with the invention, each pulse producing desirably sev eral ink drops. As shown, each pulse has a steep or rap idly rising leading edge 24 which increases from a base level 25 to a predetermined peak level 26, 3,500 volts being satisfactory for the peak level with the nozzle and ink specifically mentioned previously, and is maintained at that peak level for a brief period, I00 microseconds or longer being appropriate.

The trailing edge 28 of each pulse decreases slowly, that is, the trailing edge has a slow relaxation or decay time. Edge 28 may decrease at an exponential rate, as shown, or at a linear rate. As shown, edge 28 decreases to about the base level 25 prior to the occurrence of the next pulse. For example, where the ink droplet groups are formed 200 microseconds apart, that is, 200 micro seconds between leading pulse edges when the system is producing ink drops at the maximum rate, the trailing edge would decrease from the level 26 to the base level with a time constant of between 10 and I00 microsec onds, preferably 20. Obviously, the magnitude and duration of the pulses supplied by source 20 are proportional to the diameter of the ink dots produced on paper 16 and hence proportional to line thickness. A schematic diagram of a circuit for producing waveform 22 is shown as FIG. 4.

As described, the voltage pulses of waveform 22 are applied to the nozzle of an on-demand ink printer. In previously mentioned US. Pat. No. 3,373,437, slowly decaying voltage pulses are supplied to charging elec trodes in the path of ink drop travel of a continuous flow ink drop system. The pulses of the aforementioned patent thus act to deflect a plurality of previously formed ink drops.

It has been found that ink drop size and hence line thickness can be varied by applying an a.c. signal, such as from a.c. signal source 21 of FIG. I, to nozzle 10 while the pulses supplied thereto by source 20 are at the peak value. This a.c. signal, having a dc. level equal to the peak level 26, has a frequency of about one hundred thousand hertz. Conventional switching means (not needing description here) would be used for supplying the signal from source 21 to the nozzle 10. The composite signal supplied by sources 20 and 2] is shown as waveform 22a in FIG. 3b.

Even greater uniformity of drop size and elimination of secondary drops can be achieved, and more rapid turnon response can be achieved (less than 20 microseconds), by applying an ac. bias to nozzle 10. This embodiment of the invention is shown in FIG. 2. The alternating-current signal from source 30 would have a peak value substantially lower than that required to draw ink from nozzle 10, for example, about 1,000 volts peak, and would have a high frequency, preferably about five hunderd thousand hertz. The a.c. signal supplied by source 30 is applied to nozzle 10 only when the video signal supplied by circuit 20 is at about the base level. The composite waveform supplied to nozzle 10 of FIG. 3 by sources 20 and 30 would be waveform 22b shown in FIG. 3c, and the composite waveform supplies to nozzle 10 of FIG. 2 by sources 20, 21, and 30 would be waveform 226 shown in FIG. 3d. Conventional circuitry (not needing description here) would be used to open and close switch 32 in accordance with whether the signal supplied by source 20 is at about the base line level 25.

The dc. component of the a.c. bias signal need not be at the base level 25 but may be at a greater level provided that the a.c. bias signal does not of itself produce a flow of ink drops from nozzle 10.

While the invention has been described with reference to preferred embodiments thereof, it will be apparent to those skilled in the art that various changes may be made without departing from the true spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. A fluid printer in which substantially all ink drops produced are used for printing on a recording medium comprising:

a nozzle containing a conductive fluid,

an electrode disposed adjacent said nozzle and maintained at a fixed potential, and

pulsing means for applying to said nozzle a voltage waveform having a voltage pulses of sufficient magnitude to produce an electrostatic field between said nozzle and said electrode of sufficient magnitude to overcome the liquid surface tension of the nozzle and draw ink from the nozzle to the recording medium. each of said pulses having a peak amplitude portion and a trailing edge portion that decrease in magnitude at a variable rate.

2. The printer of claim 1 in which said variable rate is exponential.

3. A fluid printer in which all ink drops produced are used for printing on a recording medium comprising:

a fluid-containing nozzle,

an electrode disposed adjacent said nozzle and maintained at a fixed potential, and

pulsing means for applying to said nozzle a waveform having voltage pulses of sufficient magnitude to produce an electrostatic field between said nozzle and said electrode of sufficient magnitude to overcome the liquid surface tension of the nozzle and draw ink from the nozzle to the recording medium, each of said pulses having a peak amplitude portion and a trailing edge portion that changes in magnitude at a rate slower than the rate of the rise time of the leading edge of each of the pulses.

4. The printer of claim 3 in which said trailing edge of each pulse decreases at an exponential rate.

5. The printer of claim 3 further comprising first means for applying a first alternating current signal to said nozzle when each of said pulses is at the peak smplitude, and second means for applying a second alternating current signal to said nozzle when each of said pulses has an amplitude substantially less than said peak amplitude.

6. The printer of claim 5 in which said second alternating current signal has a frequency greater than the frequency of said first alternating current signal.

7. In a fluid printer which utilizes electrostatic field forces to project an electrically conductive fluid across a gap between a nozzle containing the fluid and a re- 6. cord medium maintained at a reference potential, the improvement comprising:

pulsing means for applying to said nozzle a waveform having voltage pulses with each pulse having a leading edge portion, a peak amplitude portion. and a trailing edge portion occurring after the peak amplitude portion, said leading edge portion having a rise time from a base value that is faster than the decay time of said trailing edge portion to about said base value, and

additional means for applying a first alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said peak amplitude.

8. The printer of claim 7 further comprising second means for applying a second alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said base value, the frequency of said second signal is greater than the frequency of said first signal.

9. The printer of claim 7 further comprising means for applying an alternating current signal to said nozzle only when the amplitude of each of said pulses is substantially lower than said peak amplitude.

10. in a fluid printer which utilizes electrostatic field forces to project an electrically conductive fluid across a gap between a nozzle containing the fluid and a record medium maintained at a reference potential, the improvement comprising:

pulsing means for applying to said nozzle a waveform having voltage pulses with each pulse having a leading edge portion, a peak amplitude portion, and a trailing edge portion occurring after the peak amplitude portion said leading edge portion having a rise time from a base value that is faster than the decay time of said trailing edge portion to about said base value, and

additional means for applying an alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said base value.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,893,131

DATED July 1, 1975 |NVENTOR(5) Julius Perel et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown betow:

Claim 5, line 4, change "smplitude" to amplitude Signed and Sealed this fourteenth Day of October 1975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (11mm issr'unvr ufParenrs and Trademarks 

1. A fluid printer in which substantially all ink drops produced are used for printing on a recording medium comprising: a nozzle containing a conductive fluid, an electrode disposed adjacent said nozzle and maintained at a fixed potential, and pulsing means for applying to said nozzle a voltage waveform having a voltage pulses of sufficient magnitude to produce an electrostatic field between said nozzle and said electrode of sufficient magnitude to overcome the liquid surface tension of the nozzle and draw ink from the nozzle to the recording medium, each of said pulses having a peak amplitude portion and a trailing edge portion that decrease in magnitude at a variable rate.
 2. The printer of claim 1 in which said variable rate is exponential.
 3. A fluid printer in which all ink drops produced are used for printing on a recording medium comprising: a fluid-containing nozzle, an electrode disposed adjacent said nozzle and maintained at a fixed potential, and pulsing means for applying to said nozzle a waveform having voltage pulses of sufficient magnitude to produce an electrostatic field between said nozzle and said electrode of sufficient magnitude to overcome the liquid surface tension of the nozzle and draw ink from the nozzle to the recording medium, each of said pulses having a peak amplitude portion and a trailing edge portion that changes in magnitude at a rate slower than the rate of the rise time of the leading edge of each of the pulses.
 4. The printer of claim 3 in which said trailing edge of each pulse decreases at an exponential rate.
 5. The printer of claim 3 further comprising first means for applying a first alternating current signal to said nozzle when each of said pulses is at the peak smplitude, and second means for applying a second alternating current signal to said nozzle when each of said pulses has an amplitude substantially less than said peak amplitude.
 6. The printer of claim 5 in which said second alternating current signal has a frequency greater than the frequency of said first alternating current signal.
 7. In a fluid printer which utilizes electrostatic field forces to project an electrically conductive fluid across a gap between a nozzle containing the fluid and a record medium maintained at a reference potential, the improvement comprising: pulsing means for applying to said nozzle a waveform having voltage pulses with each pulse having a leading edge portion, a peak amplitude portion, and a trailing edge portion occurring after the peak amplitude portion, said leading edge portion having a rise time from a base value that is faster than the decay time of said trailing edge portion to about said base value, and additional means for applying a first alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said peak amplitude.
 8. The printer of claim 7 further comprising second means for applying a second alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said base value, the frequency of said second signal is greater than the frequency of said first signal.
 9. The printer of claim 7 further comprising means for applying an alternating current signal to said nozzle only when the amplitude of each of said pulses is substantially lower than said peak amplitude.
 10. In a fluid printer which utilizes electrostatic field forces to project an electrically conductive fluid across a gap between a nozzle containing the fluid and a record medium maintained at a reference potential, the improvement comprising: pulsing means for applying to said nozzle a waveform having voltage pulses with each pulse having a leading edge portion, a peak amplitude portion, and a trailing edge portion occurring after the peak amplitude portion, said leading edge portion having a rise time from a base value that is faster than the decay time of said trailing edge portion to about said base value, and additional means for applying an alternating current signal to said nozzle only when each of said pulses supplied to said nozzle by said pulsing means is substantially at said base value. 